This is what the call center told me. I am performing signal integrity measurements and don't have a symmetrical fixture with any measurement data to de-embed with. So, we talked about using port extensions and time domain gating and it was mentioned that port extensions was only good to about 2 GHz. Was just wondering...have to make measurements out to 20 GHz.

For loss and delay, it is no problem to use port extensions to 20 GHz. Mismatch will not be compensated for, but time domain can remove mismatch effects pretty well. Have you considered PLTS? It is specifically intended to support Signal Integrety applications.